A Long-Term Evolution (LTE) system is standardized by Third Generation Partnership Project (3GPP) as a global standard wireless communication technology. 3GPP and Next Generation Mobile Networks (NGMN) have discussed self-organizing network (SON) aimed at reduction in operational cost of operators and at automatic network optimization in an LTE system. SON features are classified into four categories: planning, development, optimization, and maintenance (Non Patent Literature 1, 2, and 3). By applying SON features for efficient operation, construction, and planning of a network, such as wireless communication parameter optimization, network parameter optimization, and addition of a neighbor cell list, network stability is expected to improve.
In particular, implementation of self-configuration process and self-optimization process by automating tasks that have conventionally been done manually by operators can minimize the network operation cost. A self-configuration process is defined as a process to automatically obtain basic parameters necessary for system operation and to perform configuration when a base station (evolved Node B (eNB)) is newly installed. This self-configuration process is considered as a process that is mainly performed before the base station transitions to an operational state.
A self-optimization process is defined as a process to perform automatic network adjustment on the basis of statistical data from a terminal user equipment (UE) and/or the base station. This self-optimization process is considered as a process that is initiated after a radio frequency (RF) device starts up and is performed when the base station is in an operational state. Examples of parameter processed by a self-optimization process include the amount of transmitted power, the antenna tile angle of the wireless base station, and neighbor cell information. To achieve the object as described above, the self-optimization process appropriately modifies one or multiple of these wireless communication parameters in the wireless base station and/or in an operational management server (operation, administration, and maintenance (OAM) server or SON server).
Technology relating to coverage optimization will be described below with reference to Patent Literature 1. FIG. 11 is a diagram for explaining a technology relating to optimization of coverage over two macro-cells. It is assumed in FIG. 11 that base stations (eNB1, eNB2) in macro-cells are connected to an operational management server (OAM/SON server) and that a certain UE resides in a macro-cell (Cell1) and is in communication with the base station 1 (eNB1).
The base station eNB1 instructs the UE to measure reception quality of the downlink reference signal (known signal) from the base station eNB1 and reception quality of the downlink reference signal from a base station eNB (e.g., the base station 2 (eNB2)) in a near cell, and to provide a report if a predetermined specific condition is satisfied. On the basis of the instruction from the base station eNB1, the UE measures reception quality of the downlink reference signal, and then reports the measurement result of the reception quality of the downlink reference signal to the base station eNB1 (Measurement report). The base station eNB1 reports the measurement result received from the UE to the OAM/SON server (Report). In the example of FIG. 11, the base station eNB2 also similarly reports, to the OAM/SON server, the measurement result received from a UE managed by the base station eNB2. After reception of the measurement result reports from the base stations eNB1 and eNB2, the OAM/SON server instructs the base stations eNB1 and eNB2 to adjust wireless communication parameters and the like for coverage optimization. (Adjustment for Optimization). For example, the base stations eNB1 and eNB2 each make adjustments to the amount of transmitted power and/or to the antenna tile angle of the cell of the base station to perform coverage optimization on the basis of the instruction from the OAM/SON server to adjust wireless communication parameters etc. for wireless coverage optimization.